A fluxgate 1 is a type of magnetic field sensor used for detecting a buried object containing iron such as a mine and for an electronic compass.
A basic structure of the fluxgate 1 comprises a ferromagnetic body 2, a drive coil 4 surrounding the ferromagnetic body 2, a separate pickup coil 5, an AC power supply 3 for applying an alternating current to the drive coil 4, and a voltmeter 6 for detecting a voltage induced in the pickup coil 5 as shown in FIGS. 1 and 3. The components may be located on a printed circuit board 8.
The operation principle of the fluxgate 1 is as follows. When the AC current is applied to the drive coil 4 winded on the ferromagnetic body 2, a time-varying induction magnetic field is generated around the coil 4, particularly in the coil 4, and the ferromagnetic body 2 is magnetized by the time-varying induction magnetic field to become an electromagnet having an N pole and an S pole. Since the induction magnetic field has a time-variance reversed according to a time, a magnetic pole of the ferromagnetic body 2 disposed in the coil 4 is also reversed according to the time, and a magnetic field formed by the ferromagnetic body 2 around the fluxgate 1 also varies according to the time. An induction current is generated by time-varying induction magnetic field, and a voltage wave or a voltage peak is detected in the pickup coil 5 as the time varies as shown in FIGS. 2 and 5.
FIG. 1 illustrates a conventional tri-axis fluxgate 7. The conventional fluxgate 7 has a structure wherein three fluxgates 1 are perpendicular to one another in order to measure a direction of an applied magnetic field such as a terrestrial magnetism. The fluxgate 7 shown in FIG. 1 operates in a following manner. A drive coil 4 and a pickup coil 5 are simultaneously winded on two bar-type magnetic bodies 2, i.e. a pair of bar-type magnetic bodies per axis of x, y and z axes. Thereafter, a pyramidal wave or a sinusoidal wave is inputted to the drive coil 4 to magnetize the two bar-type magnetic bodies 2 in different directions, and a voltage waveform detected at the pickup coil 5 simultaneously winded on the two bar-type magnetic bodies is read. (a) of FIG. 2 illustrates an input voltage waveform applied to magnetic bodies A and B of the two bar-type fluxgates having a structure shown in (b) of FIG. 1. A current inputted according to an identical drive coil is applied such that the magnetic bodies A and B are magnetized in the different directions.
(b) of FIG. 2 illustrates an output voltage waveform detected at the pickup coil winded on the two bar-type fluxgates. A solid line output waveform denoted as ‘A’ is a signal generated from the magnetic body A, and a dotted line output waveform denoted as ‘B’ is a signal generated from the magnetic body B. Pickup voltages of the two bar-type fluxgates have different polarity as shown in (b) of FIG. 2. The reason that the output voltage is similar to the input voltage as shown in (b) of FIG. 2 is that the conventional fluxgate uses a bulk-type magnetic body manufactured by binding a ferromagnetic bar or a ferromagnetic powder using an epoxy contrary to the present invention wherein a semiconductor technology is used. Therefore, a magnetic characteristic of the magnetic body is poor and the magnetic reversal of the magnetic body is imperfect, thereby electrically behaving as a simple transformer. The conventional product has a characteristic wherein the output wave is the pyramidal wave when the input wave is the pyramidal wave, and the output wave is the sinusoidal wave when the input wave is the sinusoidal wave.
A state shown in (b) of FIG. 2 illustrates an output signal when no external magnetic field is applied. As shown, when two signals are added, a state of ‘O’ volt is obtained by cancelling the voltage outputs having different polarities. A state shown in (c) of FIG. 2 illustrates an output signal detected in the conventional fluxgate when an external magnetic field is applied. A horizontal is relatively generated in the output voltage signal to generate a new output voltage from the state of ‘O’ volt/ the conventional fluxgate has the structure wherein two bar-type fluxgates are arranged per x, y and z axes, and each of the fluxgates generates the new output voltage as the magnetic field is applied.